Hydraulic transmission



Jan. 21, 1941. w MERRlLL HYDRAULIC TRANSMISSION Filed Dec. 17, 1958 2 Sheets-Sheet l INVENTOR.

.Fan. 21, 1941 w. P. MERRILL HYDRAULIC TRANSMISSION Filed Dec. 1'7, 1938 2 Sheets-Sheet 2 IN V EN TOR.

R mm VQ w mm w QQ /WW R \w WQ Patented Jan. 21, 1941 PATENT OFFICE HYDRAULIC TRANSMISSION Wesley P. Merrill, Milwaukee, Wis., assignor to The Oilgear Company, Milwaukee, Wis., a corporation of Wisconsin Application December 17, 1938, Serial No. 246,275

6 Claims.

, This invention relates. to a hydraulic transmission of the type which includes a rotary hydraulic motor and a variable displacement pump.

A transmission of this type is sometimes employed to drive a shaft or the like which tends to overrun and drive the motor under certain conditions of operation or during a part of a. revolution. For example, the crank of a crankshaft or the cam of a camshaft may oppose rotation of theshaft until the crank or cam passes dead center in respect to the load and then the load will react upon the crank or cam and tend to drive the shaft, thereby causing the shaft to tend to drive the prime mover that .drives it and to take up all the backlash in theegearing between the driving motor and the shaft.

The above mentioned objectionable characteristics have heretofore been overcome by connecting a resistance valve and a by-pass valve into the return side of the circuit and so arranging and controlling the by-pass valve that the motor must discharge through the resistance valve until pump displacement exceeds a predetermined value and then the by-pass valve is shifted to permit 25 the liquid discharged by the pump'to flow freely therethrough to the pump, as disclosed in application Serial No. 137,738, filed April 19, 1937, by Walter Ferris, issued June 25, 1940, as Patent No. 2,205,647.

In the apparatus disclosed in the above application, the by-pass valve is shifted magnetically in response to pump displacement being increased beyond a predetermined value. l The present invention has as an object to pro- 35 vide a transmission of the above character with a by-pass valve which is operated automatically so that the motor discharge is unrestricted unless the load tends to overrun and drive the motor and then the by-pass valve operates to direct the motor discharge through the resistance valve regardless of pump, displacement or motor speed.

Another object is to enable the operator to reduce pump displacement to zero and to apply a brake load upon the motor by operating a single control element.

Other objects and advantages will appear from the following description of the hydraulic transmissions shown schematically in the accompanying drawings in which the views are as follows:

Fig. 1- is a diagrammatic view showing the invention incorporated in a hydraulic transmission which is employed to drive a blanking press, the several parts being shown in the positions occupied when the press is idle,

Fig. 5 is a view showing the control valve shifted to a position different than that shown in Fig. 4.

For the purposeof illustration. the invention has been shown as being employed to drive a blanking press but it is to be understood that it 15 may as readily be employed to drive any rotating member which has a tendency to overrun during a given part of each revolution or under certain conditions of operation, such for example as the camshaft of a knitting machine in which rollers are urged by springs against the cams on the shaft.

FIGS. 1 To 3 The press chosen for illustration is adapted to have an upper die I fixed to a platen 2 which is fitted for vertical reciprocation between guides or ways 3 carried by the frame 4 of the press. Platen 2 is connected by a link 5 to the crank pin 6 of a crankshaft l which is journaled in the upper end of frame 4 and has fixed thereon a gear wheel 8 and a flywheel 9. Shaft I when rotated will cause platen 2 to be reciprocated vertically along guides 3 and move die I toward and from a lower die I0 which is carried by frame 4.

Power for driving the press is transmitted .35 thereto through a hydraulic motor l2 which has been shown arranged upon a bracket I 3 carried by frame 4. Motor I2 is provided with a driving pinion M which meshes with gear wheel 8 so that, when motor I 2 is energized, it will rotate gear wheel 8 and crankshaft i and thereby reciprocate platen 2.

The die carried by the platen of a press of this type is often so large and heavy that, as soon as the crank pin passes upper dead center, the combined weight of the platen and the upper die is great enough to cause the crankshaft to overrun and tend to drive the prime mover that drives it. This tendency of the crankshaft to overrun does no harm during normal operation of the press and is overcome by the inertia of flywheel 9 when the press is performing useful work. However, before the dies are finally adjusted, it is essential that the upper die be lowered until it is just clear of the lower die, then the dies be carefully adjusted, and then the upper die be slowly lowered into the lower die for the reason that a pair of blanking dies have a very close fit one with the other and, if the upper die strikes the lower die, one or both of the dies are ruined or at least damaged. In order to prevent crankshaft I from overrunning, motor I2 is caused to discharge through a resistance valve whenever shaft 1 tends to overrun as will presently appear.

Motor I2 is driven by liquid supplied thereto through a pressure channel l5 by a variable displacement pump l6 which has been shown as being driven by an electric motor I! and arranged therewith upon a reservoir l8 from which pump I6 is supplied with liquid through a channel not shown.

A pump which may be employed for this pur pose is shown in Patent No. 2,033,464. This pump is provided, as is customary, with a relief valve which will open when pump pressure hecomes excessive. Pump displacement is varied by a hydraulic servo-motor which is operated by liquid supplied thereto by an auxiliary pump under the control of a follow-up valve so that a variation in pump displacement is always proportional to the distance through which the valve is moved. The valve is shifted by means of a stem which extends outward through the pump casing and has been designated in Fig. 1 by reference numeral l9.

Since 'pump l6 needs to deliver liquid in but one direction, a stop is arranged upon stem l9 and so adjusted that it will abut the end of the valve casing when pump displacement is zero.

For the purpose of.illustration, valve stem I 9 has been shown as being connected at its outer end to a control lever 2| by a pivot 22.-

Lever 2| is pivoted upon a pin 23 carried by a slide 24 which is fitted in a normally stationary guide and urged against the right end thereof by a spring 25. Guide 25 is fixed in a. stationary position as by being fastened to a bracket 21 attached to reservoir Hi. The lower end of lever 20 extends below slide. 24 and carries the movable contact of an electric switch 28.

The arrangement is such that, when the upper end oflever 2| is moved toward the left, lever 2| will pivot upon pin 23 and move valve stem I9 toward the left, thereby causing pump IE to deliver liquid through channel l5 to motor l2 at a rate proportional to the distance stem I9 is moved from the position shown in Fig. l.

Thereafter, when the upper end of lever 2| is moved toward the right as from the position shown in Fig. 4, lever 2| will pivot upon pin 23 and move valve stem l9 toward the right to gradually reduce the displacement of pump l6 until stop 20 abuts'the end of the valve casing at which time pump l6 has been adjusted to zero displacement and no liquid will be delivered thereby.

Since stop 20 prevents further movement of valve stem l9 toward the right, further movement of the upper end of lever 2| toward the right will cause lever 2| to swing upon pivot 22 and move pin 23 and slide block 24 toward the left against the resistance of spring 26 until switch 28 is closed as shown in Fig. 3, suitable stops being provided to limit the movement of slide 24 to thereby prevent switch 28 from being damaged.

The liquid discharged by pump l6 energizes motor I2 and causes it to drive the press. The liquid discharged by motor I2 is caused to flow either through a low pressure resistance valve 3|.

through a high pressure resistance valve 32 which functions as a brake valve, or through a by-pass valve 33 which has its valve member 34 fitted in a'valve casing 35 and urged toward closed position by a spring 36 the tension of which may be adjusted by a screw 31. Valve member 34 is adapted to be moved to open position as shown in Fig. 4 by liquid supplied to the lower end of casing 35 through a channel 38 which is connected to pressure channel l5 intermediate the ends thereof.

In order that the liquid discharged by motor l2 may be forced through brake valve 32, there is provided a blocking valve 39' which has its valve member 40 fitted in a casing 4|. and urged toward open position by spring 42. Valve member 40 is adapted vto be moved to closed position as shown in Fig. 2 by a solenoid 43 which has its core connected by a stem 44 to valve member 40, one end of its winding connected by a con ductor 45 to one side of a power line 46 and the other end of its winding connected by a conductor 41 to one stationary contact of switch 28 the other stationary contact of which is connected by conductor 48 to the other side of power line 46.

Motor |2 has its outlet connected by a channel 5| to blocking valve casing 4| at a point intermediate the ends thereof. By-pass valve casing 35 is connected at a point intermediate the ends thereof to one end of a channel 52 the other end of which is connected to blocking valve casing 4| at a point spaced from channel 5|. Pump l6 has its intake connected by a return channel 53 to by-pass valve casing 35 at a point spaced from channel 52. Resistance valve 3| has its inlet connected to channel 52 and its outlet connected to return channel 53. Brake valve 32 has its inlet connected to channel 5| and its outlet connected to return channel 53.

Operation When electric motor I! is driving pump I6 and control lever 2| is in its neutral position as shown in Fig. 1, pump 6 will be at zero stroke and no liquid will be delivered thereby so that motor l2 will be idle, by-pass valve 33 will be held closed by its spring 36, and switch 28 will be open so that blocking valve 39 will be held open by its spring 42.

If the dies are to be adjusted, the upper end of control lever 2| is moved slightly toward the left. Pump I5 will then deliver liquid at a limited rate through channel |5 to motor l2 and cause it to rotate crankshaft I slowly, pressur will extend from channel |5 through channel 38 to the lower end of valve casing 35 and raise valve member 34 to open communication between channels 52 and 53, and the liquid disthe rate it is being driven by pump l6 and causing the pressure in channels I5 and 38 to drop so that spring 36 can close by-pass valve 33. Then the liquid discharged by motor |2 will flow from channel 52 into channel 53 through resistance valve 3| which has sufficient resistance (ill til

to prevent motor l2 from being driven by the combined weight of platen 2 and die Motor 2 will continue to rotate crankshaft I at a slow rate until die I is just clear of die l and then lever 2| is returned to its neutral positionto reduce the displacement of pump [6 to zero and thereby stop the press so that the dies may be adjusted relative to each other.

After the dies have been properly adjusted, the upper end of lever 2| may be moved slightly toward the left to cause pump l6 to deliver liquid at a very limited rate and thereby cause die I to be lowered very slowly into die I0 to check the adjustment. Then the upper end of lever 2| may be swung farther toward the left to cause the press to operate at high speed.

The press may be stopped at any time or at the end of each cycle of operation by moving lever 2| to its neutral position, or it may be permitted to operate continuously by leaving lever 2| in its operative position.

During high speed operation of the press, the inertia of flywheel 9 ordinarily prevents the weight of platen 2 and die I from causing the pressure in channel to drop sufficiently to permit by-pass valve 33 to close. However, if bypass valve 33 should close due to the weight of platen 2 and die I tending to drive motor I2, no

harm or delay would result as the resistance of valve 3| would cause the pressure in channel l5 to immediately rise and reopen by-pass valve 33.

If an emergency should arise, such as a work piece being improperly located upon die III or too many work pieces being fed simultaneously between the dies, the press may be stopped very quickly by swinging the upper end of control lever 2| toward the right to the limit of its movement.

Lever 2| would at first swing upon pin 23 until valve stem l9 reached the limit of its movement as determined by stop 20 and then it would swing upon pivot 22 and shift slide 24 till switch 28 was closed.

Shifting valve stem 9 to the limit of its movement toward the right would cause the displacement of pump IE to be reduced to zero as previously explained. Closing switch 28 would cause solenoid 43 to be energized and to close blocking valve 39 so that all liquid discharged by motor I2 would be forced to pass through brake valve 32 which has suflicient resistance to very quickly decelerate the press to a complete stop.

FIGS. 4 AND 5 The apparatus shown in Fig. 4 is the same as the apparatus shown in Fig. 1 except that the blocking valve is operated hydraulically instead of mechanically. Consequently, like parts have been indicated by like reference numerals and only a brief description is deemed necessary.

Communication between channels 5| and 52 is controlled by a blocking valve 39 the valve member'Ml of which is fitted in a casing 4| and urged upward or toward open position by a spring 42*.

Valve member 4|! is adapted to be moved downward or to closed position by liquid delivered to the upper end of casing from a gear pump 59 which draws liquid from a reservoir 50 and discharges continuously through a. channel 6| and a relief valve 62 into reservoir 60.

For the purpose of illustration, gear pump 59 and relief valve 82 have been shown separate from pump l6 but in practice both are arranged inside the casing of pump I6, and gear pump 59 is driven in unison with pump l6 according to the usual practice and as shown in Patent No. 2,033,464 referred to above.

Delivery of liquid to the upper end of blocking valve casing 4| is under the control of a pilot valve 63 which is fitted in a stationary valve casing 64 and urged against the right end thereof by a spring 65.

Valve casing 64 has formed therein a port 66 which is connected to gear pump discharge channel 6| and normally blocked by valve 63, a port 61 which is connected to a drain channel 68, and a port 69 which is arranged between ports 66 and 61 and connected by a channel to the upper end of blocking valve casing 4| Valve 63 has a stem 1| connected by a pin 23 to the lower end of a control lever 2| which is connected by pivot 22 to the control valve stem IQ of pump I6.

Spring 65 normally holds valve 63 against the right end of valve casing 54 so that pin 23* remains stationary and lever 2| may pivot thereon to vary pump displacement in the previously described manner.

During normal operation of the press, port 66 -is blocked by valve 63 and port 69 is open to port 61 so that the pressure in the upper end of valve casing H is zero and spring 42 is thus able to hold blocking valve 39 open.

The apparatus functions exactly the same as the apparatus shown in Fig. 1 functions. If an emergency should arise, the operator would swing the upper end of lever 2| toward the right. Lever 2| would pivot upon pin 23 until valve stem l9 reached the limit prescribed by stop 20 and then lever 2| would turn upon pivot 22 and shift valve 63 toward the left to the position shown in Fig. 5, thereby closing port 61 and openingport 66 to port 69 so that liquid from gear pump 59 could flow through channel 10 to the upper end of valve casing M and move valve member 4|] downward to close communication between channels 5| and 52 as shown in Fig. 2.

' The liquid discharged by motor 2 must then pass through brake valve 32 as previously explained.

The invention herein set forth is susceptible of various modifications and adaptations without departing from the scope thereof as hereafter claimed.

The invention is hereby claimed as follows:

1. The combination. with a shaft having a, tendency to overrun during at least a part of a revolution, of a hydraulic motor connected to said shaft to drive the same, a power driven pump for supplying motive liquid to said motor to energize the same, fluid channels connecting said pump and said motor and forming therewith a hydraulic circuit having pressure and return sides, a low pressure resistance valve connected into one part of the return side of said circuit to resist the discharge of liquid from said motor and thereby prevent said shaft from overrunning, a high pressure resistance valve connected in parallel with said valve to provide a high resistance to the discharge of liquid from said motor and thereby function as a braketo stop said motor and said shaft, a bypass valve connected into another part of said return side and adapted when open to by-pass around" said resistance F valves the liquid discharged by saidmotor, means responsive to the pressure of the liquid in the pressure side of said circuit exceeding a predetermined value for opening said by-pass valve, and

other means separately operable for causing all of the liquid discharged by said motor to pass through said high pressure resistance valve.

2. The combination, with a shaft having a tendency to overrun during at least a part of a revolution, of a hydraulic motor connected to said shaft'to drive the same, a power driven pump for supplying motive liquid to said motor to energize the same, fluid channels connecting said pump and said motor and forming therewith a hydraulic circuit having pressure and return sides, a low pressure resistance valve connected into one part of the return side of said circuit to resist the discharge of liquid from said motor and thereby prevent said shaft from overrunning, a high pressure resistance valve connected in parallel with said valve to provide a high resistance to the discharge of liquid from said motor and thereby function as a brake to stop said motor and said shaft, a by-pass valve connected into another part of said return side and adapted when open to by-pass around said resistance valves the liquid discharged by said motor, means responsive to the pressure of the liquid in the pressure side of said circuit exceeding a predetermined value for opening said bypass valve, a normally open fourth valve connected into the return side of said circuit and adapted when closed to cause all of the liquid discharged by said motor to pass through said high pressure resistance valve, and means for closing said fourth valve. 1

3. The combination, with a shaft having a tendency to overrun during at least a part of a revolution, of a hydraulic motor connected to said shaft to drive the same, a power driven pump for supplying motive liquid to said motor to energize the same, fluid channels connecting said pump and said motor and forming ,therewith a hydraulic circuit having pressure and return sides, a low pressure resistance valve connected into one part of the return side of said circuit to resist the discharge of liquid from said motor and thereby prevent said shaft from overrunning, a high pressure resistance valve connected in parallel with said valve to provide a high resistance to the discharge of liquid from said motor and thereby function as a brake to stop said motor and said shaft, a by-pass valve connected into another part of said return side and adapted when open to by-pass around said resistance valves the liquid discharged by said motor, means responsive to the pressure of the liquid in the pressure side of said circuit exceeding a predetermined value for opening said bypass valve, means for varying the displacement of said pump to thereby vary the speed of said motor, and means responsive to a part of said displacement varying means being moved to a given point for causing all of the liquid discharged by said motor to pass through said high pressure resistance valve. 7

4. The combination, with a shaft having a tendency to overrun during at least a part of a revolution, of a hydraulic motor connected to said shaft to drive the same, a power driven pump for supplying motive liquid to said motor to energize the same, fluid channels connecting said pump and said motor and forming therewith a hydraulic circuit having pressure and return sides, a low pressure resistance valve connected into one part of the return side of said circuit to resist the discharge of liquid from said motor and thereby prevent said shaft from overrunning, a high pressure resistance valve connected in parallel withsaid valve to provide a high resistance to the discharge of liquid from said motor and thereby function as a brake to stop said motor and said shaft, a by-pass valve connected into another part ofsaid return side and adapted when open to by-pass around said resistance valves the liquid discharged by said motor, means responsive to the pressure of the liquid in the pressure side of said circuit exceeding a predetermined value for opening said by-pass valve, means for varying the displacement of said pump to thereby vary the speed of said motor, a normally open fourth valve connected into the return side. of said circuit and adapted when closed to cause all of the liquid discharged by said motor to pass through said high pressure resistance valve, and means responsive to a part of said displacement varying means being moved to a given point for closing said fourth valve.

5. The combination, with a shaft having a tendency to overrun during at least a part of a revolution, of a hydraulic motor connected to said shaft to drive the same, a power driven pump for supplying motive liquid to said motor to energize the same, fluid channels connecting said pump and said motor and forming therewith a hydraulic circuit having pressure and return sides, a low a pressure resistance valve connected into one part of the return side of said circuit to resist the discharge of liquid from said motor and thereby prevent said shaft from overrunning, a high pressure resistance valve connected in parallel with said valve to provide a high resistance to the discharge of liquid from said motor and thereby function as a brake to stop said motor and said shaft, a by-pass valve connected into another part of said return side and adapted when open to by-pass around said resistance valves the liquid discharged by said motor, means responsive to the pressure of the liquid in the pressure side of said circuit exceeding a predetermined value for opening said by-pass valve, means for varying the displacement of said pump to thereby vary the speed of said motor, a normally open fourth valve connected into the return side of said circuit and adapted when closed to cause all of the liquid discharged by said motor to pass through said high pressure resistance valve, a solenoid for'closing said fourth valve, a switch for energizing said solenoid, and means responsive to a part of said displacement varying means being moved to a given point for closing said switch.

6. The combination, with a shaft having a tendency to overrun during at least a part of a revolution, of a hydraulic motor connected to said shaft to drive the same, a power driven pump for supplying motive liquid to said motor to energize the same, fluid channels connecting said pump and said motor and forming therewith a hydraulic circuit having pressure and return sides, a low pressure resistance valve connected into one part of the return side of said circuit to resist the discharge of liquid from said motor and thereby prevent said shaft from overrunning, a high pressure resistance valve connected in parallel with said valve to provide a high resistance to the discharge of liquid from said motor and thereby function as a brake to stop said motor and said shaft, a by-pass valve connected into another part of said return side and adapted when open to opening said by-pass valve, means for varying the displacement of said pump to thereby vary the speed of said motor, a normally .open fourth valve connected into the return side of said circuit and adapted when closed to cause all of the liquid discharged by said motor to pass through 

